Method of removing carbonic-acid gas from nitrogen gas.



H. PHILIPP. METHOD OF REMOVING CARBONIC ACID GAS FROM NITRO GEN GAS.

APPLICATION FILED JUNE 30. I914 Patented Sept 11, 1917.

g, i g y;

ns amnir ent ies HERBERT PHILIP; OF PERTH AMBY, NEW JERSEY, ASSIGND;.

HASSLACHER CHEMICAL 00., OF N EW YORK", N. Y., A CORPORATION OF NEW YORK.

METHOD or REMOVING cARBon c-Aom GAS mica NITROGEN Gas.

resident of the city of Perth Amboy, county of lviiddlesex, and State of New Jersey, have invented certain new and useful Improvements in Methods of Removing Carbonic- Acid Gasfrom Nitrogen Gas, of which the following is a specification.

i My invention relates to the production of pure nitrogen gas and has particular reference to a method of purifying a mixture of nitrogen and other gases y means of absorbents. In the manufacture of pure, nitrogen gas various methods have been followed, one of said methods being-the removal of carbonic acid gas by the combustion of a mixture of gas and air with the intention of obtaining pure nitrogen I gas.

The removal of carbonic acid gas has, however, mostly been effected by passing the gas mixture through suitable containers charged with milk of lime, whereby carbonic acid gas has been absorbed, more or less pure nitrogen gas remaining at the end ofthe operation.

I have found, however, that in the manufacture ofnitrogen gas on a larger scale, the complete absorption of carbon dioXid gas from the mixture is by no means an easy matter, and that milk of lime does not so readily combine with small quantities of carbon dioxid, unless the height of the column of milk of lime is beyond practical methods. Of course several containers charged with milk of lime can be used, connected in series, but even then it is found that to remove the last traces of carbon dioxid a very large number of containers have to be used in series, the number being outof,proportion to the carbon dioxid in the gas. An example will explain this; an impure nitrogen gas (for instance flue gas) containing l82l% CO when passed through a ten foot column of milk of lime, will still contain from 347% C0 if the gas from this container is passed through a second container with a ten foot column of lnilk of lime in it, it will be found that only very little. of the remaining carbon dioxid has been removed or combined with the cal cium liydroxid, as the gas from this last container contains still 24% ("0 1 It is well known that a solution otflan alkali hydroxid a. {/..-sodium hydroxid, will Specification of Letters Patent.

Patented Sept. 11, 1191?.

Application filed June 30, 1914. Serial No. 848,134.

readily and quantitatively absorb carbon dioXid, forming sodium carbonate, but on account of the facility with which sodium carbonate crystallizes out, a method based on a reaction of this nature is impossible on a large scale as impractical and too expensive. N ow 1 have found that by the additionof a relatively small quantity of a suitable substance of basioreaction, as for instance of an alkali hydroxid or carbonate, to the milk of lime, as for instance sodium hydroxid or carbonate, a very considerable increase in the power of in the gas is obtained. It may be that the addition of sodium hydroxid to the milk of lime causes primarily a formation of sodium carbonate which beingpresent only in a very small quantity, instantaneously reacts with TO THE ROESSLER &'

the excess of lime present, being rcconverted The reactions represented by the above,

equations go on alteri'iately and follow each other'of course at indefinitely short intervals and in quick succession. The milk of lime obviously obtains by my new process constant absorption power, that is, it absorbs carbonic acid gas equally well, regardless of whether the milk of lime contains 30% CaO or 1% or less C210. I have found by numerous tests that the content of sodium hy droxid remains constant during the process of absorption, while the content of calcium hydroxid gradually diminishes. Thus for instance, if a milk of lime is prepared by slaking 1200 lbs. commercial lime in 3000 lbs. of water, and to this a small quantity of commercial caustic soda is added (0. 9. about 5 lbs.) it has been found that the solution will test approximately 2830% Ca() and 0.1% NaOll. The content of sodium hy droxid remains consl ant during the process of absorption until all the calciiun hydroxid hasbcen converted into calcium carbonate. Thus tests near the end of the absorption process, while giving a gas practically tree lests during the process ot absorption show ever) time Ithe same amount of available sodufun hydroxnl. In contrast to the milk of ill) lime alone, a gas as described above when passed through a ten foot column of milk of lime containing a very small quantity of sodium hydroxid, will test 0.51.0% CO and if this gas is then passed through a second similarly charged container connected in series with the first one, then it is found that the gas is free from carbon dioxid, and consists,'in this case, of nitrogen, moisture and perhaps a trace of oiiygen; the two latter constituents being removed by known methods, a pure nitrogen gas is thus produced.

' ient temperature to hold the milk of lime at is ratus through pipe 1 and passes thence into the bottom of a scrubber 2 and up through the same against a descending flow of water entering the scrubber at the top through pipe 3. The gas is washed and cooled in the scrubber by the descending water and.

the temperature of the gas lowered to about 20-25 C. Scrubber 2 is connected by pipe 4 to the suction end-of pump 5. The dis charge end of pump 5 is connected by pipe 6 with main 7 in turn connected with lime agitators or containers 8 and 9 by pipes 10 and 11 respectively. 12 is the discharge pipe from lime agitator 8 and is cross connected to pipe 11 by pipe 13 and with discharge pipe 14 from agitatorl) as shown.

15 is a pipe cross connecting entrance pipe 10 to discharge pipe 14. All of said pipes are suitably valve controlled as shown. The

two lime agitators are preferably connected in series with each other through pipes 6, 7

10, 12, 13 and 11 and discharge through pipes 14 and 12 into a series of tubes 16, 17,

.18-and 19 each containing copper heated to about 650-7 00 C. The gas enters the lower tube 1", thence through pipe 20 into tubc .17 and ti ence into main 21 which leads to a drier 22. 23 is a pipe connecting pipe 12 with tube 18 and 24 is a pipe connecting tube 18with tube 19. 25 is a pipe connecting tube 19 with main 21. 26 is a pipe connecting with pipe 12 and 27 is a. branch from I have found that the most conven pipe 26 connecting with pipe 23. All of said pipes are suitably valve controlled as shown.

The gas passes from drier 22 through pipe 28 to meter 29 and thence is distributed wherever it is required. As shown the gas may be passed in series through tubes 16 and 17, or through tubes 18 and 19, as desired, or otherwise as the connections permit and the operation may be repeated as desired.

The lime agitators are preferably filled with a solution of 25 to 30% CaO containing a small quantity of sodium hydroxid in the proportion of 200-2410 pants CaO to one part of NaOH. The scrubber is filled with suitable filling material overwhich water is run to cool the gases that they may enter the pump at a low temperature. In passing through the agitators the gases give off all their, carbonic acid gas to the sodium hydroxid and calcium hydroxid respectively and are then passed into the highly heated copper tubes to be freed of their small content of oxygen. The importance of the addition of alkali hydroxid to the quick-lime solutlon 1s very great forwhereas I formerly never succeeded in getting nitrogen free from carbonic acid gas, as is desirable formany operations, I now succeed by the continuous regenerating of sOdium hydroxid as described in completely absorbing the car- 2. The method of removing carbonic acid gas from nitrogen consisting in passing the impure gas through milk of lime containing a small quantity of an alkali metal hydroXid.

The method of removing carbonic acid gas from nitrogen gas, consisting inpassing the impure gas through milk of lime containinga small quantity of sodium hydroxid.

In testimony whereof I have signed this specification in the presence of two subscribing witnesses.

' HERBERT PHILIPP.

Witnesses: i

CATHERINE A. Cos'rnLLo, Orro K. Zwmcuunnnenu. 

